The present invention relates generally to the field of steam generator cleaning, and in particular to a new and useful apparatus and method for removing sludge from and obtaining access to the interbundle region of a steam generator chamber or other similar confined spaces.
In nuclear power stations, steam generators, such as recirculating steam generators and once through steam generators, are used for heat exchange purposes in the generation of steam to drive the turbines. Primary fluid which is heated by the core of the nuclear reactor passes through a bundle of tubes in the steam generator. Secondary fluid, normally water, which is fed into the space surrounding the tubes, receives heat from the tubes and is converted into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes and on the tubesheet which supports same. The sludge is comprised mainly of an iron oxide such as magnetite, and reduces the heat transfer efficiency of the tubes and can cause corrosion. Thus, the tubes must be cleaned periodically to remove the sludge. Various types of apparatus and method are available to accomplish this task.
It is often advantageous to removably insert lances, which may carry water lines, video cameras and other items, into steam generator chambers for cleaning, inspection and testing. However, in order to reach the far walls of the generator chamber or into interior chambers between the heat exchange tubes, relatively elongated flexible lances are required. Support for the lances and other items is required to accurately direct the operating ends within the steam generator for intertube cleaning, inspection, and/or maintenance. The space adjacent the exterior of steam generators in nuclear plants is usually limited due to other considerations. Extremely long, inflexible lances and supports have limited utility since storage during non-use is difficult or impossible.
Related information on sludge lances can be found in the disclosures of U.S. Pat. Nos. 4,980,120 to Bowman et al.; U.S. Pat. Nos. 5,411,043, 5,509,609, and 5,570,969 to Kamler; and U.S. Pat. Nos. 5,555,851, 5,570,660, and 5,572,957 to Vandenberg.
It is an object of the present invention to provide a lance for insertion into a nuclear steam generator which is supported inside the steam generator, but which can be stored conveniently in a limited space outside of the steam generator.
It is a further object of the invention to provide a support for a lance or other elongated structure which is flexible outside of the steam generator, but rigid inside the steam generator.
Accordingly, a lance having a segmented support is provided that can be removably inserted through a wall of a nuclear steam generator by a linear motor. The lance has an articulated head at one end which is first inserted into the steam generator chamber. The support has left and right side segments. The segments of each side are pivotally joined together. The joints of the left and right sides pivot opposite those of the other side, and the joints between the segments are horizontally offset from each other. One side of the segments may be nested inside the other around the lance.
The lance and segments are fed into the steam generator by a single linear motor through an opening in the steam generator wall. The segments of each support side may be coiled prior to feeding. One end segment on each side is fastened near the end of the lance adjacent the articulated head. The articulated head extends past the support and may be moved relative to the remainder of the supported lance to direct a working end of the lance at a particular work surface for inspection, cleaning, maintenance or testing.
In an alternate embodiment of the support, a series of rigid segments having a channel support for the lance are joined by hinges which permit folded storage of the support outside the steam generator chamber. The hinges may be locked when the support is in use immediately prior to insertion through the steam generator chamber wall. Similarly, a single linear guide motor may be used or two motors employed to insert the lance and support through the chamber wall. An articulated head extends from the end of the rigid support inside the steam generator.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.